The present invention relates to a prosthetic limb having a regenerative and electronically controlled prosthetic joint. More specifically, the present invention is directed to a prosthetic leg having a regenerative and electronically controlled knee joint capable of converting mechanical energy, normally dissipated during the gait cycle, into electrical energy. The electrical energy may either be used as generated, or may be stored for later use. Stored electrical energy can be subsequently released as necessary to assist with an amputee's gait cycle or to provide power to various other electrical energy consuming devices associated with the amputee.
Lower limb amputations can be classified as one of two types: below knee (BK), or above knee (AK). A below knee amputation occurs along a line through the tibia and fibula of the lower leg; with the knee joint remaining intact. An above knee amputation, however, is a transfemoral amputation; meaning that the knee joint is also removed.
Constructing a prosthetic limb for an AK amputee is a more complicated process than constructing one for a BK amputee. A BK prosthesis is fitted to the amputee's residual leg, with the amputee's knee joint providing necessary bending during the gait cycle. However, as the natural knee joint has been removed from an AK amputee, an AK prosthesis must be constructed to simulate knee flexion and extension if the amputee's gait when using the prosthesis is to have any semblance of normality.
To this end, typical AK prosthetic legs have been constructed with a flexible (hinged) joint connecting a lower leg portion to an upper socket portion which, in turn, fits to the amputee's residual leg. Such a prosthetic leg allows the amputee to freely swing the lower leg portion forward during the extension portion of the gait cycle, and also allows for the lower leg portion to fold backward during the flexion portion of the gait cycle. Such simplistic artificial knee joints can be problematic, however. For example, failure to fully swing the lower leg portion forward during the extension portion of the gait cycle can result in instability, as the knee joint may unexpectedly and undesirably bend under the amputee's weight. In addition to these drawbacks, the vaulting motion and subsequent flexion of the knee joint relies solely on energy input from the amputee and the resulting momentum of the gait cycle. Such knee joint operation can be very difficult for the amputee to control—especially as energy and momentum build. Further, using a prosthetic limb with such a knee joint can require a significant expenditure of energy, which may be especially difficult for elderly or infirm amputees.
In an attempt to better control the gait cycle of an AK prosthetic leg, both basic and electronically controlled passive knee joints have been developed. These knees employ devices such as pneumatic and hydraulic cylinders, magnetic particle brakes, and other similar damping mechanisms, to damp energy generated during the gait cycle so that the prosthetic leg moves through a more controlled range of motion. These damping devices also offer resistance to bending of the knee joint, thereby providing additional stability. Such devices must be designed and/or adjusted based on an amputee's weight, gait pattern, and activity level, among other factors. In the case of an electronically controlled passive prosthetic knee, a software enabled microprocessor and one or more sensors are typically used to monitor the gait cycle of the amputee and adjust the damping device accordingly.
While AK prosthetic legs employing these passive prosthetic knee joints are an improvement over limbs using earlier free-swinging knee joints, such legs still rely solely on energy input from the amputee and the resulting momentum of the gait cycle for their operation. Electronic control systems associated with these passive prosthetic knee joints also require a power source, such as a battery, for their operation.
Most known AK prosthetic legs typically focus on optimizing two specific indices of the gait cycle. The first of these indices is generally referred to as “heel rise,” and can be described as the angle to which the knee flexes after the toe leaves the floor. During active gait, and without the affect of some restraining force, the heel can rise so far as to prevent it from properly traveling forward later in the gait cycle. Typical AK prosthetic limbs attempt to limit heel rise to around 60 degrees in order to best mimic normal gait.
The other focus of many known AK prosthetic limbs is typically referred to as “terminal impact.” As the leg travels forward, the lower (shin) portion thereof swings towards an extended position and can obtain relatively high angular speeds relative to the thigh portion. Terminal impact is, therefore, defined as the impact that the lower portion of the prosthetic leg imparts to the rest of the prosthetic frame when it reaches its full extension and stops—usually just before the foot contacts the ground. Dissipation of this energy can result in a hammering effect on the frame potion of the prosthetic leg that is both uncomfortable for the amputee, and potentially destructive to the prosthesis.
The need for a highly active AK prosthetic leg to limit heel rise and terminal impact requires significant energy consumption by the amputee. The faster an amputee walks, the faster the prosthetic leg must move and the more energy the amputee must impart to the prosthetic leg. Unfortunately, much of the energy that is imparted to the prosthetic leg is lost on the next half step, either at the end of heel rise, or at terminal impact.
Various devices and methods have been developed to dissipate this energy. The most common of these devices and methods are friction, pneumatic, hydraulic, or magneto-rheological braking systems that simply convert the dissipated energy to heat. The result of using such devices and methods is that the faster an amputee tries to walk, the more energy they waste in each step. In effect, the amputee is penalized by the prosthesis for higher levels of activity because the energy cost per step rises rapidly with speed. For this, and other reasons, gait tends to be relatively slow in all but the most healthy and motivated AK amputees.
The aforementioned AK prosthetic legs also suffer from other drawbacks. For example, it has been found that, due to the significant energy input required, only a select few AK amputees are able to ascend stairs in a leg over leg manner using a prosthetic leg having a passive knee joint. Simply put, due to the lack of the natural knee joint and corresponding muscles, most AK amputees lack the strength necessary to ascend stairs in a conventional manner using a prosthetic leg with a passive knee joint.
In an attempt to alleviate these and other problems associated with known passive prosthetic knee joints, active prosthetic knee joints have been proposed. However, up until now these active prosthetic knee joints have suffered from various deficiencies including, among other things, the lack of accurate control, the lack of an acceptable actuator for imparting energy to the amputee's gait cycle, and the inability to produce a sufficient power supply for proposed actuators that can also be easily transported. For example, there have been proposals for hydraulically or pneumatically powered active prosthetic knee joints. Such designs have several drawbacks including, for example, the likelihood of leaks in the actuator or supply lines to the actuator, the build up of heat from repeated movement of the actuator, and problems associated with producing an acceptably sized portable hydraulic or pneumatic pump to power the actuator. Noise levels associated with operation of a power supply for such an actuator are also problematic. It has been further proposed to construct an active prosthetic knee joint using an electric motor(s). However, an external power supply is also required to power such a prosthetic knee joint. Additionally, proposed power supplies have been bulky, and cannot be comfortably or easily transported by an amputee. In a similar manner to the suggested hydraulically or pneumatically powered prosthetic knee joint, the proposed electrically powered knee joints have also been overly noisy.